Air filtration is a necessity in many industrial and commercial environments, not only for the health, comfort and safety of personnel, but also to prevent deposition of dust, lint, or other airborne material on heat exchanging elements of air conditioning equipment, on process equipment, or in or onto processed materials or products. Various types of self-cleaning filters are in use, principally (a) filter wall arrangements with traveling indexing suction cleaners; (b) filter walls comprised of filter paper strips stretched between rolls for automatic feeding of fresh paper as the porous paper loads up with dust, with the loaded paper being discarded; (c) rotating drum filters in which the dust is collected on the outside of the drum and is cleaned off by a suction nozzle traversing the length of the rotating drum; and (d) stationary drum filters which collect the dust on the drum and have rotating suction nozzles for covering the entire length of the drum at each rotation, as illustrated in U.S. Pat. No. 3,887,344.
Each of the above filtration systems has its own drawbacks, e.g.:
(a) the filter wall can only have the filtration area determined by the cross-sectional area of the duct or chamber within which it is installed; and while an indexing, traversing suction cleaning nozzle is mechanically practical, it is comparatively expensive and unwieldy; PA1 (b) a filter wall comprised of throw-away paper strips has the same filter area limitations as the filter wall discussed above; constant paper replacement is expensive; and air flow tends to concentrate at the area of least resistance where fresh paper is fed in; PA1 (c) rotating drum filters are unwieldy and require large amounts of floor space because of the large amount of open and wasted space inside the drum; and PA1 (d) stationary drum filters have the suction cleaning apparatus located inside the drum for rotation while the drum remains stationary, but the suction cleaning nozzles typically have a total length corresponding to the entire length of the drum thereby requiring a large amount of high suction air to meet the demands of the nozzles, and they also require large amounts of floor space.
The stationary cylindrical cell filter of the present invention effectively overcomes the aforesaid objections to the prior art filters by combining a stationary drum and rotating suction nozzle with a traversing nozzle in a simple apparatus; and by its suitability for forming a filter wall comprising a composite filter bank of reasonably sized filter units providing an equal filtration area in a much smaller floor space than that required by the prior art rotating and stationary filter drums discussed above and providing a significantly greater filtration area in only a little more floor space than required by the two prior art filter walls discussed above, while significantly cutting the volume of high suction air required for cleaning the filter and, at the same time, permitting the forming of a filter wall of any size and shape.